The present invention relates to a starter with a protection device, and more particularly, to a starter with an electric protection device for protecting an internal combustion engine against damage resulting from rapid repeated starting. A starter switch initiates a starting process, in the course of which a pinion is advanced on the armature shaft of an electric starter motor by an engagement relay and is meshed into a ring gear of the internal combustion engine. A contact bridge for supplying main current to the starter motor is closed by a meshing armature of the engagement relay. The protection device is supplied, after an aborted attempt at starting, that is to say when the starter switch is opened and the main current supply of the starter motor is disconnected, by a voltage which is induced by the rotation of the armature shaft of the coasting starter motor.
Internal combustion engines, in particular engines for motor vehicles, have to be started by a starter since they cannot start under their own power as can electric motors. The starter must rotate the internal combustion engine at a minimum starting speed of revolution and, after the first ignitions, support the engine as it runs up to the minimum independent speed of revolution. The considerable resistances of sealing, piston friction and bearing friction have to be overcome. Electric D.C. series-wound motors are preferably used as starters since they develop the required initial torque. The torque is transmitted to the flywheel on the crankshaft of the internal combustion engine via a pinion and a ring gear. As soon as the internal combustion engine starts and accelerates beyond the starting speed of revolution under its own power, the connection between starter shaft and crankshaft must be automatically eliminated in order to protect the starter, and the pinion must be unmeshed. Therefore, starters are equipped with a free-wheel, and a meshing and return mechanism.
The high degree of stressing of the starter when the pinion is meshed into the ring gear leads to damage to the ring gear in the event of incorrect operation. Two possible types of incorrect operation are to be noted as causes.
A first cause is rapid repeated starting after a false start. That is, as a result of rapid repeated starting, after a preceding unsuccessful attempt at starting, the coasting pinion strikes the already stationary starter ring gear and therefore cannot mesh. The result is mechanical abrasion of the teeth with typical damage to the ring gear. The abrasion can be seen at the 2 swing-out positions in the case of the 4-cylinder engine or the 3 swing-out positions in the case of the 6-cylinder engine.
A second cause is repeated starting when the engine is already running. That is, if the driver has not noticed that the engine has started and attempts restarting, the pinion strikes the rotating ring gear and cannot mesh. The result is equally typical damage in which the abrasion is distributed over the entire circumference of the ring gear.
A conventional starter with a protection device is shown in DE-Z: BOSCH, Technische Unterrichtung: Startanlagen (Technical instruction aid: Starting systems, 1984, pp. 9 and 32) in which a start-blocking relay prevents the starter motor being switched on when the engine is running or coasting after a false start. Repeated starting is not possible until an integrated blocking time has elapsed. The start-blocking relay operates as a function of the voltage of a current generator or of a tacho-generator.
A further protection device is disclosed in DE-A 2 208 045 in which a voltage brought about by the rotation of the armature shaft of the starter motor is additionally evaluated. This voltage can be generated inductively for example in an auxiliary winding or in the case of a series-wound D.C. motor in the exciter winding by the rotation of the armature shaft. The voltage increases with the speed of revolution of the armature shaft and is connected to the input of a threshold-value switch which switches off the starter motor when the minimum independent speed of revolution of the internal combustion engine is reached. In order to prevent, after a false start, the pinion being meshed into the ring gear when the starter motor is still coasting, a blocking time which is determined by a capacitor, within which time an attempt at starting is ignored, is provided as in the case of the start-blocking relay already mentioned above.
Both of these known protection devices are capable of preventing damage to the ring gear and to the pinion which is caused by the two incorrect operations explained above. However, these protection devices are complex and expensive due to the large number of relays and components used in their construction. Since they are made as a separate module which is separated from the starter motor, they also require increased cabling outlay, as well as additional feedlines from the generator or rev-counter and, if appropriate from an auxiliary winding in the starter motor. This outlay is acceptable if the starting process cannot be reliably perceived audibly, for example in utility vehicles with underframe-mounted or rear-mounted engine.
The avoidance of damage resulting from excessively rapid repeated starting after a false start is a prime consideration especially for passenger cars, since the starting process can be monitored acoustically and repeated starting therefore occurs less-frequently when the engine is already running. A starter with a simple protection device which performs this function is described in the JP Abstract 63-302174 (A), M-809 4 Apr. 1989 in which the blocking time for repeated starting is controlled by a voltage which is induced by the coasting of the armature shaft. For this purpose, the protection device is supplied, after an aborted or unsuccessful attempt at starting and, in the process, disconnected main power supply of the starter motor, by a voltage which is induced by the rotation of the armature shaft of the coasting starter motor. As long as the armature shaft coasts and a voltage is applied to the protection device, a contact bridge in the main current supply line remains opened so that repeated starting cannot occur. A disadvantage of this known protection device is the comparatively long blocking time resulting from the coasting time of the starter motor and a requirement of an additional current switching relay to disconnect the main current supply.
An object of the present invention is to provide a starter with a simple and cost-effective protection device which permits rapid repeated starting after a false start and at the same time ensures that the pinion is at rest during engagement.
This object has been achieved in accordance with the present invention by providing a system after an aborted attempt at starting, the pinion meshed in the ring gear for as long as the protection device is supplied by the voltage induced by the rotation of the coasting armature shaft, with the contact bridge remaining disconnected.
The present invention uses the starter motor as a generator after an aborted start and disconnected main current supply with the coasting starter motor in order to feed a protection device with the induced voltage. The device keeps the pinion in engagement with the ring gear for the coasting time. As a result, the pinion is not unmeshed until the starter motor has come to a standstill. In the event of rapid repeated starting, the pinion is therefore either still meshed or at rest. The cause which leads to the first mentioned damage discussed above, i.e. a still rotating pinion striking a stationary ring gear, is thus excluded.
The second mentioned damage, which is caused by an attempt at meshing the already started internal combustion engine into a rotating ring gear, is also reduced. That is, after a successful start, the pinion does not unmesh until, due to the free-wheel between armature shaft and pinion, the armature shaft of the switched-off starter motor comes to a standstill and current no longer flows through the protection device. Provisional measurements show that the pinion remains meshed in the ring gear one to two seconds longer. During this time period, erroneous repeated starting in the running engine is possible without abrasion occurring at the ring gear.
A further advantage of the protection device according to the present invention resides in the fact that the time after which repeated starting can take place under the same initial conditions as a first start is shortened. The armature shaft of the starter motor is actually very rapidly braked by the coasting internal combustion engine. Normally, the pinion coasting time would be five to six times as long as the coasting time of the internal combustion engine. The shortening of the waiting time until possible repeated starting is also important for safety considerations since the traffic situation often requires rapid repeated starting.
Further advantages of the solution according to the present invention result from the structure hereinafter described. The protection device is realized in a very simple and robust manner by a stop armature with electromagnetic drive.